High-density plasma source

ABSTRACT

The present invention relates to a plasma source. The plasma source includes a cathode assembly having an inner cathode section and an outer cathode section. An anode is positioned adjacent to the outer cathode section so as to form a gap there between. A first power supply generates a first electric field across the gap between the anode and the outer cathode section. The first electric field ionizes a volume of feed gas that is located in the gap, thereby generating an initial plasma. A second power supply generates a second electric field proximate to the inner cathode section. The second electric field super-ionizes the initial plasma to generate a plasma comprising a higher density of ions than the initial plasma.

BACKGROUND OF INVENTION

Plasma is considered the fourth state of matter. A plasma is acollection of charged particles that move in random directions. A plasmais, on average, electrically neutral. One method of generating a plasmais to drive a current through a low-pressure gas between two conductingelectrodes that are positioned parallel to each other. Once certainparameters are met, the gas “breaks down” to form the plasma. Forexample, a plasma can be generated by applying a potential of severalkilovolts between two parallel conducting electrodes in an inert gasatmosphere (e.g., argon) at a pressure that is in the range of about10⁻¹ to 10⁻² Torr.

Plasma processes are widely used in many industries, such as thesemiconductor manufacturing industry. For example, plasma etching iscommonly used to etch substrate material and to etch films deposited onsubstrates in the electronics industry. There are four basic types ofplasma etching processes that are used to remove material from surfaces:sputter etching, pure chemical etching, ion energy driven etching, andion inhibitor etching.

Plasma sputtering is a technique that is widely used for depositingfilms on substrates and other work pieces. Sputtering is the physicalejection of atoms from a target surface and is sometimes referred to asphysical vapor deposition (PVD). Ions, such as argon ions, are generatedand are then drawn out of the plasma and accelerated across a cathodedark space. The target surface has a lower potential than the region inwhich the plasma is formed. Therefore, the target surface attractspositive ions.

Positive ions move towards the target with a high velocity and thenimpact the target and cause atoms to physically dislodge or sputter fromthe target surface. The sputtered atoms then propagate to a substrate orother work piece where they deposit a film of sputtered target material.The plasma is replenished by electron-ion pairs formed by the collisionof neutral molecules with secondary electrons generated at the targetsurface.

Reactive sputtering systems inject a reactive gas or mixture of reactivegases into the sputtering system. The reactive gases react with thetarget material either at the target surface or in the gas phase,resulting in the deposition of new compounds. The pressure of thereactive gas can be varied to control the stoichiometry of the film.Reactive sputtering is useful for forming some types of molecular thinfilms.

Magnetron sputtering systems use magnetic fields that are shaped to trapand concentrate secondary electrons proximate to the target surface. Themagnetic fields increase the density of electrons and, therefore,increase the plasma density in a region that is proximate to the targetsurface. The increased plasma density increases the sputter depositionrate.

BRIEF DESCRIPTION OF DRAWINGS

This invention is described with particularity in the detaileddescription. The above and further advantages of this invention may bebetter understood by referring to the following description inconjunction with the accompanying drawings, in which like numeralsindicate like structural elements and features in various figures. Thedrawings are not necessarily to scale, emphasis instead being placedupon illustrating the principles of the invention.

FIG. 1 illustrates a cross-sectional view of a known plasma generatingapparatus having a direct current (DC) power supply.

FIG. 2A illustrates a cross-sectional view of a plasma generatingapparatus having a segmented cathode according to the invention.

FIG. 2B illustrates a cross-sectional view of the segmented cathode ofFIG. 2A.

FIG. 3 illustrates a cross-sectional view of a plasma generatingapparatus including a magnet assembly according to the invention.

FIG. 4 illustrates a graphical representation of applied power as afunction of time for periodic pulses applied to an initial plasma in theplasma generating system of FIG. 2A.

FIG. 5 illustrates a cross-sectional view of a plasma generatingapparatus including the magnet assembly of FIG. 3 and an additionalmagnet assembly according to the invention.

FIG. 6 illustrates a cross-sectional view of a plasma generatingapparatus including the magnet assembly of FIG. 3 and an additionalmagnet assembly according to the invention.

FIG. 7 illustrates a cross-sectional view of another embodiment of aplasma generating apparatus including a magnet assembly according to theinvention.

FIG. 8 illustrates a cross-sectional view of a plasma generatingapparatus including a magnet configuration that includes a first magnetand a second magnet according to the invention.

FIG. 9 illustrates a cross-sectional view of a plasma generatingapparatus according to the present invention including a segmentedcathode assembly, an ionizing electrode, and a first, a second and athird power supply.

FIG. 10 illustrates a cross-sectional view of a plasma generatingapparatus according to the present invention including a segmentedcathode assembly, a common anode, an ionizing electrode and a first, asecond and a third power supply.

FIG. 11 illustrates a cross-sectional view of a plasma generatingapparatus according to the present invention including a segmentedcathode assembly and a first, a second and a third power supply.

FIG. 12 illustrates a cross-sectional view of a plasma generatingapparatus according to the present invention including a segmentedcathode assembly, an excited atom source, and a first, and a secondpower supply.

FIG. 13 illustrates a graphical representation of the power as afunction of time for each of a first, a second and a third power supplyfor one mode of operating the plasma generating system of FIG. 9.

FIG. 14 illustrates a graphical representation of power generated as afunction of time for each of a first, a second and a third power supplyfor one mode of operating the plasma generating system of FIG. 9.

FIG. 15 illustrates a graphical representation of the power as afunction of time for each of a first, a second and a third power supplyfor one mode of operating the plasma generating system of FIG. 9.

FIG. 16A through FIG. 16C are flowcharts of illustrative processes ofgenerating high-density plasmas according to the present invention.

DETAILED DESCRIPTION

FIG. 1 illustrates a cross-sectional view of a known plasma generatingapparatus 100 having a DC power supply 102. The known plasma generatingapparatus 100 includes a vacuum chamber 104 where a plasma 105 isgenerated. The vacuum chamber 104 can be coupled to ground. The vacuumchamber 104 is positioned in fluid communication with a vacuum pump 106via a conduit 108 and a valve 109. The vacuum pump 106 is adapted toevacuate the vacuum chamber 104 to high vacuum. The pressure inside thevacuum chamber 104 is generally less than 10⁻¹ Torr. A feed gas 110 froma feed gas source 111, such as an argon gas source, is introduced intothe vacuum chamber 104 through a gas inlet 112. The gas flow iscontrolled by a valve 113.

The plasma generating apparatus 100 also includes a cathode assembly114. The cathode assembly 114 is generally in the shape of a circulardisk. The cathode assembly 114 can include a target 116. The cathodeassembly 114 is electrically connected to a first terminal 118 of the DCpower supply 102 with an electrical transmission line 120. An insulator122 isolates the electrical transmission line 120 from a wall of thevacuum chamber 104. An anode 124 is electrically connected to a secondterminal 126 of the DC power supply 102 with an electrical transmissionline 127. An insulator 128 isolates the electrical transmission line 127from the wall of the vacuum chamber 104. The anode 124 is positioned inthe vacuum chamber 104 proximate to the cathode assembly 114. Aninsulator 129 isolates the anode 124 from the cathode assembly 114. Theanode 124 and the second output 126 of the DC power supply 102 arecoupled to ground in some systems.

The plasma generating apparatus 100 illustrates a magnetron sputteringsystem that includes a magnet 130 that generates a magnetic field 132proximate to the target 116. The magnetic field 132 is strongest at thepoles of the magnet 130 and weakest in the region 134. The magneticfield 132 is shaped to trap and concentrate secondary electronsproximate to the target surface. The magnetic field increases thedensity of electrons and, therefore, increases the plasma density in aregion that is proximate to the target surface.

The plasma generating apparatus 100 also includes a substrate support136 that holds a substrate 138 or other work piece. The substratesupport 136 can be electrically connected to a first terminal 140 of aRF power supply 142 with an electrical transmission line 144. Aninsulator 146 isolates the RF power supply 142 from a wall of the vacuumchamber 104. A second terminal 148 of the RF power supply 142 is coupledto ground.

In operation, the feed gas 110 from the feed gas source 111 is injectedinto the chamber 104. The DC power supply 102 applies a DC voltagebetween the cathode assembly 114 and the anode 124 that causes anelectric field 150 to develop between the cathode assembly 114 and theanode 124. The amplitude of the DC voltage is chosen so that it issufficient to cause the resulting electric field to ionize the feed gas110 in the vacuum chamber 104 and to ignite the plasma 105.

The ionization process in known plasma sputtering apparatus is generallyreferred to as direct ionization or atomic ionization by electron impactand can be described by the following equation:Ar+e ⁻→Ar⁺+2e ⁻

where Ar represents a neutral argon atom in the feed gas 110 and e⁻represents an ionizing electron generated in response to the voltageapplied between the cathode assembly 114 and the anode 124. Thecollision between the neutral argon atom and the ionizing electronresults in an argon ion (Ar⁺) and two electrons.

The plasma 105 is maintained, at least in part, by secondary electronemission from the cathode assembly 114. The magnetic field 132 that isgenerated proximate to the cathode assembly 114 confines the secondaryelectrons in the region 134 and, therefore, confines the plasma 105approximately in the region 134. The confinement of the plasma in theregion 134 increases the plasma density in the region 134 for a giveninput power.

The plasma generating apparatus 100 can be configured for magnetronsputtering. Since the cathode assembly 114 is negatively biased, ions inthe plasma 105 bombard the target 116. The impact caused by these ionsbombarding the target 116 dislodges or sputters material from the target116. A portion of the sputtered material forms a thin film of sputteredtarget material on the substrate 138.

Known magnetron sputtering systems have relatively poor targetutilization. The term “poor target utilization” is defined herein tomean undesirable non-uniform erosion of target material. Poor targetutilization is caused by a relatively high concentration of positivelycharged ions in the region 134 that results in a non-uniform plasma.Similarly, magnetron etching systems (not shown) typically haverelatively non-uniform etching characteristics.

Increasing the power applied to the plasma can increase the uniformityand density of the plasma. However, increasing the amount of powernecessary to achieve even an incremental increase in uniformity andplasma density can significantly increase the probability ofestablishing an electrical breakdown condition leading to an undesirableelectrical discharge (an electrical arc) in the chamber 104.

Applying pulsed direct current (DC) to the plasma can be advantageoussince the average discharge power can remain relatively low whilerelatively large power pulses are periodically applied. Additionally,the duration of these large voltage pulses can be preset so as to reducethe probability of establishing an electrical breakdown conditionleading to an undesirable electrical discharge. An undesirableelectrical discharge will corrupt the plasma process and can causecontamination in the vacuum chamber 104. However, very large powerpulses can still result in undesirable electrical discharges regardlessof their duration.

In one embodiment, an apparatus according to the present inventiongenerates a plasma having a higher density of ions for a giving inputpower than a plasma generated by known plasma systems, such as theplasma generating apparatus 100 of FIG. 1.

A high-density plasma generation method and apparatus according to thepresent invention uses an electrode structure including three or moreelectrodes to generate a high-density plasma including excited atoms,ions, neutral atoms and electrons. The electrodes can be a combinationof cathodes, anodes, and/or ionizing electrodes. The electrodes can beconfigured in many different ways, such as a ring electrode structure, alinear electrode structure, or hollow cathode electrode structure. Theplasma generation method and apparatus of the present invention providesindependent control of two or more co-existing plasmas in the system.

A high-density plasma source according to the present invention caninclude one or more feed gas injection systems that inject feed gasproximate to one or more of the electrodes in the plasma source. Thefeed gas can be any mixture of gases as described herein. The one ormore feed gas injection systems can also inject plasma proximate to oneor more of the electrodes in the plasma source. The injected plasma canbe a high-density plasma or a low-density plasma. In one embodiment, aninitial plasma is generated and then it is super-ionized to form ahigh-density plasma. The term “super-ionized” is defined herein to meanthat at least 75% of the neutral atoms in the plasma are converted toions.

The high-density plasma source of the present invention can operate in aconstant power, constant voltage, or constant current mode. These modesof operation are discussed herein. In addition, the high-density plasmasource can use different types of power supplies to generate thehigh-density plasma. For example, direct-current (DC),alternating-current (AC), radio-frequency (RF), or pulsed DC powersupplies can be used to generate the high-density plasma. The powersupplies can generate power levels in the range of about 1 W to 10 MW.

The plasma generated by the high-density plasma source of the presentinvention can be used to sputter materials from solid or liquid targets.Numerous types of materials can be sputtered. For example, magnetic,non-magnetic, dielectric, metals, and semiconductor materials can besputtered.

In one embodiment, the high-density plasma source of the presentinvention generates relatively high deposition rates near the outer edgeof a sputtering target. The target can be designed and operated suchthat the increase in the deposition rate near the outer edge of thesputtering target compensates for the decrease of the sputtering ratetypically associated with the edge of a sputtering target. Thisembodiment allows the use of relatively small targets, which can reducethe overall footprint of a process tool, the cost of the target and thecost to operate the process tool.

The high-density plasma source of the present invention provides hightarget utilization and high sputtering uniformity. Additionally, theplasma generated by the high-density plasma source of the presentinvention can be used for producing ions or atoms from molecules fornumerous applications, such as sputter etch, reactive etch, chemicalvapor deposition, and for generating ion beams.

FIG. 2A illustrates a cross-sectional view of a plasma generatingapparatus 200 having a segmented cathode 202 according to the invention.In one embodiment, the segmented cathode 202 includes an inner cathodesection 202 a and an outer cathode section 202 b. In some embodiments(not shown), the segmented cathode 202 includes more than two sections.The segmented cathode 202 can be composed of a metal material, such asstainless steel or any other material that does not chemically reactwith reactive gases. The segmented cathode 202 can include a target (notshown) that is used for sputtering. The inner cathode section 202 a andthe outer cathode section 202 b can be composed of different materials.

The outer cathode section 202 b is coupled to a first output 204 of afirst power supply 206. The first power supply 206 can operate in aconstant power mode. The term “constant power mode” is defined herein tomean that the power generated by the power supply has a substantiallyconstant power level regardless of changes in the output current and theoutput voltage level. In another embodiment, the first power supply 206operates in a constant voltage mode. The term “constant voltage mode” isdefined herein to mean that the voltage generated by the power supplyhas a substantially constant voltage level regardless of changes in theoutput current and the output power level. The first power supply 206can include an integrated matching unit (not shown). Alternatively, amatching unit (not shown) can be electrically connected to the firstoutput 204 of the first power supply 206.

A second output 208 of the first power supply 206 is coupled to a firstanode 210. An insulator 211 isolates the first anode 210 from the outercathode section 202 b. In one embodiment, the second output 208 of thefirst power supply 206 and the first anode 210 are coupled to groundpotential (not shown).

In one embodiment (not shown), the first output 204 of the first powersupply 206 couples a negative voltage impulse to the outer cathodesection 202 b. In another embodiment (not shown), the second output 208of the first power supply 206 couples a positive voltage impulse to thefirst anode 210. Numerous types of power supplies can be used for thefirst power supply 206. For example, the first power supply 206 can be apulsed power supply, radio-frequency (RF) power supply, analternating-current (AC) power supply, or a direct-current (DC) powersupply.

The first power supply 206 can be a pulsed power supply that generatespeak voltage levels of up to about 5 kV. Typical operating voltages arein the range of about 50V to 5 kV. The first power supply 206 cangenerate peak current levels in the range of about 1 mA to 100 kAdepending on the desired volume and characteristics of the plasma.Typical operating currents vary from less than one hundred amperes tomore than a few thousand amperes depending on the desired volume andcharacteristics of the plasma. The first power supply 206 can generatepulses having a repetition rate that is below 1 kHz. The first powersupply 206 can generate pulses having a pulse width that is in the rangeof about one microsecond to several seconds.

The first anode 210 is positioned so as to form a gap 212 between thefirst anode 210 and the outer cathode section 202 b that is sufficientto allow current to flow through a region 214 between the first anode210 and the outer cathode section 202 b. In one embodiment, the width ofthe gap 212 is in the range of about 0.3 cm to 10 cm. The surface areaof the outer cathode section 202 b determines the volume of the region214. The gap 212 and the total volume of the region 214 are parametersin the ionization process as described herein.

For example, the gap 212 can be configured to generate exited atoms fromground state atoms. The excited atoms can increase the density of aplasma. Since excited atoms generally require less energy to ionize thanground state gas atoms, a volume of excited atoms can generate a higherdensity plasma than a similar volume of ground state feed gas atoms forthe same input energy. Additionally, the gap 212 can be configured toconduct exited atoms towards the inner cathode section 202 a. Theexcited atoms can either be generated externally or inside the gap 212depending on the configuration of the system. In one embodiment, the gap212 exhibits a pressure differential that forces the exited atomstowards the inner cathode section 202 a. This can increase the densityof the plasma proximate to the inner cathode section 202 a as previouslydiscussed.

The gap 212 can be a plasma generator. In this configuration, feed gasis supplied to the gap 212 and a plasma is ignited in the gap 212. Anignition condition in the gap 212 can be optimized by varying certainparameters of the gap 212. For example, the presence of crossed electricand magnetic fields in the gap 212 can assist in the ignition anddevelopment of a plasma in the gap 212. The crossed electric andmagnetic fields trap electrons and ions, thereby improving theefficiency of the ionization process.

The gap 212 can facilitate the use of high input power. For example, ashigh power is applied to a plasma that is ignited and developing in thegap 212, additional feed gas can be supplied to the gap 212. Thisadditional feed gas displaces some of the already developing plasma andabsorbs any excess power applied to the plasma. The absorption of theexcess power prevents the plasma from contracting and terminating whichcould otherwise occur without the additional feed gas.

In some embodiments (not shown), the first anode 210 and/or the outercathode section 202 b can include raised areas, depressed areas, surfaceanomalies, or shapes that improve the ionization process. For example,the pressure in the region 214 can be optimized by including a raisedarea (not shown) on the surface of the outer cathode section 202 b. Theraised area can create a narrow passage at a location in the region 214between the first anode 210 and the outer cathode section 202 b thatchanges the pressure in the region 214.

The first output 220 of a second power supply 222 is electricallycoupled to the inner cathode section 202 a. The second power supply 222can operate in a constant power mode or a constant voltage mode. Thesecond power supply 222 can have an integrated matching unit (notshown). Alternatively, a matching unit (not shown) is electricallyconnected to the first output 220 of the first power supply 222. Thesecond power supply 222 can be any type of power supply, such as apulsed power supply, a DC power supply, an AC power supply, or a RFpower supply.

A second output 224 of the second power supply 222 is coupled to asecond anode 226. An insulator 227 is positioned to isolate the secondanode 226 from the outer cathode section 202 b. Another insulator (notshown) can be positioned to isolate the second anode 226 from the innercathode section 202 a. In one embodiment (not shown), the second output224 of the second power supply 222 and the second anode 226 areelectrically connected to ground potential.

The first output 220 of the second power supply 222 can couple anegative voltage impulse to the inner cathode section 202 a. The secondoutput 224 of the second power supply 222 can couple a positive voltageimpulse to the second anode 226.

The second power supply 222 can be a pulsed power supply that generatespeak voltage levels in the range of about 50V to 5 kV. The second powersupply 222 can generate peak current levels in the range of about 1 mAto 100 kA depending on the desired volume and characteristics of theplasma. Typical operating currents varying from less than one hundredamperes to more than a few thousand amperes depending on the desiredvolume and characteristics of the plasma and the desired plasma density.The pulses generated by the second power supply 222 can have arepetition rate that is below 1 kHz. The pulse width of the pulsesgenerated by the second power supply 222 can be between about onemicrosecond and several seconds.

The second anode 226 is positioned proximate to the inner cathodesection 202 a such that current is capable of flowing between the secondanode 226 and the inner cathode section 202 a. The distance between thesecond anode 226 and the inner cathode section 202 a can be in the rangeof about 0.3 cm to 10 cm.

The plasma generating apparatus 200 can include a chamber (not shown),such as a vacuum chamber. The chamber is coupled in fluid communicationto a vacuum pump (not shown) through a vacuum valve (not shown). Thechamber can be electrically coupled to ground potential.

One or more gas lines 230, 232 provide feed gas 234, 236 (indicated byarrows) from one or more feed gas sources 238, 240, respectively, to thechamber. The feed gas lines 230, 232 can include in-line gas valves 242,244 that can control the gas flow to the chamber. The gas lines 230, 232can be isolated from the chamber and other components by insulators (notshown). The gas lines 230, 232 can be isolated from the one or more feedgas sources 238, 240 using in-line insulating couplers (not shown). Theone or more feed gas sources 238, 240 can include any feed gas, such asargon. The feed gas can be a mixture of different gases, reactive gases,or pure reactive gas gases. The feed gas can include a noble gas or amixture of gases.

In one embodiment, the in-line gas valves 242, 244 are switchable massflow controllers (not shown). The switchable mass flow controllers canbe programmed inject the feed gases 234, 236 in a pulsed manner from thefeed gas sources 238, 240, respectively. For example, the pressure inthe gap 212 can be varied and optimized by pulsing the feed gas 234 thatis injected directly into the gap 212. In one embodiment, the timing ofthe pulses is synchronized to the timing of power pulses generated bythe first power supply 206 operated in a pulsed mode. Pulsing the feedgases 234, 236 can also assist in the generation of excited atomsincluding metastable atoms in the gap 212. For example, by pulsing thefeed gas 234 in the gap 212, the instantaneous pressure in the gap isincreased while the average pressure in the chamber is unchanged.

Skilled artisans will appreciate that the plasma generating apparatus200 can be operated in many different modes. In some modes of operation,the first 206 and the second power supplies 222 together with thesegmented cathode 202 are used to generate independent plasmas. Theparameters of an initial plasma and a high-density plasma can be variedindividually as required by the particular plasma process.

In one mode of operation, the feed gas 234 from the feed gas source 238is supplied to the chamber by controlling the gas valve 242. The feedgas 234 is supplied between the outer cathode section 202 b and thefirst anode 210. The feed gas 234 can be directly injected into the gap212 between the outer cathode section 202 b and the first anode 210 inorder to increase the density of a plasma that is generated in the gap212. Increasing the flow rate of the feed gas causes a rapid volumeexchange in the region 214 between the outer cathode section 202 b andthe first anode 210. This rapid volume exchange increases the maximumpower that can be applied across the gap 212 and thus, permits ahigh-power pulse having a relatively long duration to be applied acrossthe gap 212. Applying high-power pulses having relatively long durationsacross the gap 212 results in the formation of high-density plasmas inthe region 214, as described herein.

In another mode of operation, the first power supply 206 is a componentin an ionization source that generates an initial or a pre-ionizationplasma in the region 214. The pre-ionization plasma can be aweakly-ionized plasma. The term “weakly-ionized plasma” is definedherein to mean a plasma with a relatively low peak plasma density. Thepeak plasma density of the weakly ionized plasma depends on theproperties of the specific plasma processing system. For example, aweakly ionized argon plasma is a plasma that has a peak plasma densitythat is in the range of about 10⁷ to 10¹² cm⁻³.

After a sufficient volume of the feed gas 234 is supplied between theouter cathode section 202 b and the first anode 210, the first powersupply 206 applies a voltage between the outer cathode section 202 b andthe first anode 210. The first power supply 206 can be a pulsed (DC)power supply that applies a negative voltage pulse to the outer cathodesection 202 b. The size and shape of the voltage pulse are chosen suchthat an electric field 250 (FIG. 2B) develops between the outer cathodesection 202 b and the first anode 210. The first power supply can be aDC, AC, or a RF power supply.

The amplitude and shape of the electric field 250 are chosen such thatan initial plasma is generated in the region 214 between the first anode210 and the outer cathode section 202 b. The initial plasma can be aweakly-ionized plasma that is used for pre-ionization and generally hasa relatively low-level of ionization, as described herein. In oneembodiment, the first power supply 206 generates a low power pulsehaving an initial voltage that is in the range of about 100V to 5 kVwith a discharge current that is in the range of about 0.1 A to 100 A.The width of the pulse can be in the range of approximately 0.1microseconds to one hundred seconds. Specific parameters of the pulseare discussed herein in more detail.

In another mode of operation, prior to the generation of the initialplasma in the region 214, the first power supply 206 generates apotential difference between the outer cathode section 202 b and thefirst anode 210 before the feed gas 234 is supplied to the region 214.In this mode of operation, the feed gas 234 is ignited once a sufficientvolume of feed gas is present in the region 214.

In yet another mode of operation, a direct current (DC) power supply(not shown) is used in an ionization source to generate and maintain theinitial plasma in the region 214. In this mode of operation, the DCpower supply is adapted to generate a voltage that is large enough toignite the initial plasma. For example, the DC power supply can generatean initial voltage of several kilovolts that creates a plasma dischargevoltage that is in the range of about 100V to 1 kV with a dischargecurrent that is in the range of about 0.1 A to 100 A. The value of thedischarge current depends on the power level of the DC power supply andis a function of the volume and characteristics of the plasma.Furthermore, the presence of a magnetic field (not shown) in the region214 can have a dramatic effect on the value of the applied voltage andcurrent that is required to generate the initial plasma.

The DC power supply can generate a current that is in the range of about1 mA to 100 A depending on the volume of the plasma and the strength ofa magnetic field in a region 214. In one embodiment, before generatingthe initial plasma, the DC power supply is adapted to generate andmaintain an initial peak voltage potential between the outer cathodesection 202 b and the first anode 210 before the introduction of thefeed gas 234.

In still another mode of operation, an alternating current (AC) powersupply (not shown) is used to generate and maintain the initial plasmain the region 214. An AC power supply can require less power to generateand maintain a plasma than a DC power supply. In other modes ofoperation, the initial plasma can be generated and maintained using aplanar discharge source, a radio frequency (RF) diode source, anultraviolet (UV) source, an X-ray source, an electron beam source, anion beam source, an inductively coupled plasma (ICP) source, acapacitively coupled plasma (CCP) source, a microwave plasma source, anelectron cyclotron resonance (ECR) source, a helicon plasma source, orionizing filament techniques. In some of these modes of operation, aninitial plasma can be formed outside of the region 214 and then diffusedinto the region 214.

Forming an initial plasma in the region 214 substantially eliminates theprobability of establishing a breakdown condition in the chamber whenhigh-power pulses are subsequently applied between the outer cathodesection 202 b and the first anode 210. The probability of establishing abreakdown condition is substantially eliminated because the initialplasma has at least a low-level of ionization that provides electricalconductivity through the plasma. This conductivity substantiallyprevents the setup of a breakdown condition, even when high-power isapplied to the plasma.

Referring back to FIG. 2A, the initial plasma diffuses somewhathomogeneously through the region 252 as additional feed gas 234 isinjected into the region 214. The additional feed gas 234 forces theinitial plasma from the region 214 into the region 252. This homogeneousdiffusion tends to facilitate the creation of a highly uniform plasma inthe region 252. In one embodiment, the pressure in the region 214 ishigher than the pressure in the region 252. This pressure gradientcauses the initial plasma in the region 214 to diffuse into the region252.

Once an initial plasma is formed, several modes of operation can berealized. For example, in one mode of operation, the first power supply206 generates high-power pulses in the gap 212 between the outer cathodesection 202 b and the first anode 210. The desired power level of thehigh-power pulses depends on several factors including the desiredvolume and characteristics of the plasma as well as the density of theinitial plasma. In one embodiment, the power level of the high-powerpulse is in the range of about 1 kW to 10 MW.

Each of the high-power pulses is maintained for a predetermined timethat can be in the range of about one microsecond to ten seconds. Therepetition frequency or repetition rate of the high-power pulses can bein the range of about 0.1 Hz to 1 kHz. The average power generated bythe first power supply 206 can be less than one megawatt depending onthe characteristics and the volume of the plasma. The thermal energy inthe outer cathode section 202 b and/or the first anode 210 can beconducted away or dissipated by liquid or gas cooling such as heliumcooling (not shown).

The high-power pulses generate an electric field 250 (FIG. 2B) betweenthe outer cathode section 202 b and the first anode 210. The electricfield 250 can be a relatively strong electric field, depending on thestrength and duration of the high-power pulses. The electric field 250is substantially located in the region 214 between the outer cathodesection 202 b and the first anode 210. The electric field 250 can be astatic or a pulsed electric field. In another embodiment, the electricfield 250 is a quasi-static electric field. The term “quasi-staticelectric field” is defined herein to mean an electric field that has acharacteristic time of electric field variation that is much greaterthan the collision time for electrons with neutral gas particles. Such atime of electric field variation can be on the order of ten seconds. Inanother embodiment, the electric field can be an alternating electricfield. The term “alternating electric field” is defined herein to meanthat the polarity of the electric field changes with time. The strengthand the position of the electric field 250 are discussed in more detailherein.

The high-power pulses generate a high-density plasma from the initialplasma. The term “high-density plasma” is also referred to as a“strongly-ionized plasma.” The terms “high-density plasma” and“strongly-ionized plasma” are defined herein to mean a plasma with arelatively high peak plasma density. For example, the peak plasmadensity of the high-density plasma is greater than about 10¹² cm⁻³. Thedischarge current that is formed from the high-density plasma can be onthe order of about 5 kA with a discharge voltage that is in the range ofabout 50V to 500V for a pressure that is in the range of about 5 mTorrto 10 Torr.

The high-density plasma tends to diffuse homogenously in the region 252.The homogenous diffusion creates a more homogeneous plasma volume. Thepressure gradient responsible for this homogenous diffusion is describedin more detail herein. Homogeneous plasma volumes are advantageous formany plasma processes. For example, plasma etching processes usinghomogenous plasma volumes accelerate ions in the high-density plasmatowards the surface of the substrate (not shown) being etched in a moreuniform manner than conventional plasma etching. Consequently, thesurface of the substrate is etched more uniformly. Plasma processesusing homogeneous plasma volumes can achieve high uniformity without thenecessity of rotating the substrate.

Magnetron sputtering systems using homogenous plasma volumes accelerateions in the high-density plasma towards the surface of the sputteringtarget in a more uniform manner than conventional magnetron sputtering.Consequently, the target material is deposited more uniformly on asubstrate without the necessity of rotating the substrate and/or themagnetron. Also, the surface of the sputtering target is eroded moreevenly and, thus higher target utilization is achieved. In oneembodiment, target material can be applied to the first 210 and/or thesecond anode 226 to reduce possible contamination from sputteringundesired material.

Referring back to FIG. 2A, the second power supply 222 can be a pulsedpower supply that generates high-power pulses between the inner cathodesection 202 a and the second anode 226 after the high-density plasma isformed in the region 214 and diffuses into the region 252 proximate tothe inner cathode section 202 a. The desired power level of thehigh-power pulses depends on several factors including the volume andother characteristics of the plasma such as the density of thehigh-density plasma. In one embodiment, the power level of thehigh-power pulse is in the range of about 1 kW to 10 MW.

Each of the high-power pulses is maintained for a predetermined timethat can be in the range of one microsecond to ten seconds. Therepetition frequency or repetition rate of the high-power pulses can bein the range of between about 0.1 Hz and 1 kHz. The average powergenerated by the second power supply 222 can be less than one megawattdepending on the desired volume and characteristics of the plasma. Thethermal energy in the inner cathode section 202 a and/or the secondanode 226 can be conducted away or dissipated by liquid or gas coolingsuch as helium cooling (not shown).

The high-power pulses generate an electric field 254 (FIG. 2B) betweenthe inner cathode section 202 a and the second anode 226. The electricfield 254 can be a pulsed electric field, a quasi-static electric fieldor an alternating electric field. The strength and the position of theelectric field 254 will be discussed in more detail herein.

The second power supply 222 generates high power pulses that launchadditional power into the already strongly ionized plasma and,therefore, super-ionize the high-density plasma in the region 252. Thedischarge current can be on the order of 5 kA with a discharge voltagethat is in the range of about 50V to 500V for a pressure that is in therange of about 5 mTorr to 10 Torr.

In another mode of operation, an initial plasma is generated in theregion 214 and the initial plasma diffuses to the region 252 asadditional feed gas is supplied to the region 214.

In this mode of operation, the gap 212 is dimensioned to create apressure differential between the region 214 and the region 252. Thepressure differential forces the initial plasma that is generated in theregion 214 into the region 252. In this embodiment, the second powersupply 222 applies high-power pulses between the inner cathode section202 a and the second anode 226 after a suitable volume of initial plasmais present in the region 252. The high-power pulses create an electricfield 254 between the inner cathode section 202 b and the second anode226 that strongly-ionizes the initial plasma thereby creating ahigh-density plasma in the region 252.

In yet another mode of operation, feed gas 236 from the feed gas source240 flows between the second anode 226 and the inner cathode section 202a at various times during the plasma generation process. This additionalfeed gas 236 can be a noble gas, a reactive gas, or a mixture of gases.The additional feed gas 236 can facilitate a more efficient plasmageneration process and/or can result in a higher density plasma.

In still another mode of operation, a voltage generated by the secondpower supply 222 is sufficient to ignite a second plasma (not shown)from the feed gas 236 in the region 255 between the second anode 226 andthe inner cathode section 202 a. This second plasma flows from theregion 255 into the region 252 as the second plasma is displaced by morefeed gas 236. Additionally, the second plasma from the region 255 cancommingle with the initial plasma from the region 214 in the region 252.In one embodiment, a plasma diverting plate 256 (FIG. 2B) is disposedproximate to the second anode 226 to divert the second plasma from theregion 255 toward the inner cathode section 202 a and/or towards theregion 214. The size, shape, and location of the plasma diverting plate256 depend on the desired plasma properties of the second plasma. In oneembodiment, target material can be applied to the plasma diverting plate256 to reduce possible contamination from sputtering undesired material.

Controlling the flow of the feed gases 234, 236 through the regions 214,255, respectively, can affect the homogeneity, distribution profile, anddensity of the plasma. Additionally, controlling certain parameters,such as power and pulse rate of the first 206 and the second powersupplies 222 (FIG. 2A) can also affect the homogeneity, distributionprofile, and density of the plasma.

The plasma generating apparatus 200 of the present invention generates arelatively high electron temperature plasma and a relativelyhigh-density plasma. One application for the high-density plasma of thepresent invention is ionized physical vapor deposition (IPVD) (notshown), which is a technique that converts neutral sputtered atoms intopositive ions to enhance a sputtering process.

FIG. 2B illustrates a cross-sectional view of the segmented cathode ofFIG. 2A. Specifically, FIG. 2B shows that one or both of the electricfields 250, 254 can facilitate a multi-step ionization process of thefeed gases 234, 236, respectively, that substantially increases the rateat which the high-density plasma is formed. At least one of the feedgases 234, 236 can be a molecular gas. The electric fields 250, 254enhance the formation of ions in the plasma. The multi-step or stepwiseionization process is described as follows with reference to theelectric field 250 between the outer cathode section 202 b and the firstanode 210.

A pre-ionizing voltage is applied between the outer cathode section 202b and the first anode 210 across the feed gas 234 to form an initialplasma. The initial plasma can be a weakly-ionized plasma as previouslydiscussed. The initial plasma is generally formed in the region 214 anddiffuses or is transported to the region 252 as the feed gas 234continues to flow. In one embodiment (not shown), a magnetic field isgenerated in the region 214 and extends proximate to the center of theinner cathode section 202 a. This magnetic field tends to assist indiffusing electrons in the initial plasma from the region 214 to theregion 252. The electrons in the initial plasma are substantiallytrapped in the region 252 by the magnetic field. The volume of initialplasma in the region 214 can be rapidly exchanged with a new volume offeed gas 234.

After the formation of the initial plasma in the region 214, the firstpower supply 206 (FIG. 2A) applies a high-power pulse between the outercathode section 202 b and the first anode 210. This high-power pulsegenerates the electric field 250 in the region 214. The electric field250 results in collisions occurring between neutral atoms, electrons,and ions in the initial plasma. These collisions generate numerousexcited atoms in the initial plasma. The excited atoms can include atomsthat are in a metastable state.

The accumulation of excited atoms in the initial plasma alters theionization process. The electric field 250 can be a strong electricfield that facilitates a multi-step ionization process of an atomic feedgas that significantly increases the rate at which the high-densityplasma is formed. The multi-step ionization process has an efficiencythat increases as the density of excited atoms in the initial plasmaincreases. The strong electric field 250 enhances the formation of ionsof a molecular or atomic feed gas.

In one embodiment, the dimensions of the gap 212 between the outercathode section 202 b and the first anode 210 are chosen so as tomaximize the rate of excitation of the atoms. The value of the electricfield 250 in the region 214 depends on the voltage level applied by thefirst power supply 206 and the dimensions of the gap 212. In someembodiments, the strength of the electric field 250 can be in the rangeof about 2V/cm to 10⁵ V/cm depending on various system parameters andoperating conditions of the plasma system.

The size of the gap 212 can be in the range of about 0.30 cm to 10 cmdepending on various parameters of the desired plasma. In oneembodiment, the electric field 250 in the region 214 is rapidly appliedto the initial plasma. The rapidly applied electric field 250 can begenerated by applying a voltage pulse having a rise time that is in therange of about 0.1 microsecond to ten seconds.

In one embodiment, the dimensions of the gap 212 and the parameters ofthe applied electric field 250 are varied in order to determine theoptimum condition for a relatively high rate of excitation of the atomsin the region 214. Since an argon atom requires energy of about 11.55 eVto become excited, the applied electric field 250 can be adjusted tomaximize the excitation rate of the argon atoms. As argon feed gas 234flows through the region 214, the initial plasma is formed and many ofthe atoms in the initial plasma then become excited by the appliedelectric field 250. Thus, the vast majority of ground state feed gasatoms are not directly ionized, but instead undergo a stepwiseionization process.

The excited atoms in the initial plasma then encounter electrons thatare in the region 214. In the case of argon feed case, excited argonatoms only require about 4 eV of energy to ionize while argon groundstate atoms require about 15.76 eV of energy to ionize. Therefore, whenenergy is applied in the region 214, the excited atoms will ionize at amuch higher rate than the ground state atoms. Ions in the high-densityplasma strike the outer cathode section 202 b causing secondary electronemission from the outer cathode section 202 b. These secondary electronsinteract with neutral or excited atoms in the high-density plasma. Thisprocess further increases the density of ions in the high-density plasmaas the feed gas 234 is exchanged.

The multi-step ionization process corresponding to the rapid applicationof the electric field 250 can be described as follows:Ar+e ⁻→Ar*+e ⁻Ar*+e ⁻→Ar⁺+2e ⁻

where Ar represents a neutral ground state argon atom in the feed gas234 and e⁻ represents an ionizing electron generated in response to aninitial plasma, when sufficient voltage is applied between the outercathode section 202 b and the first anode 210. Additionally, Ar*represents an excited argon atom in the initial plasma. The collisionbetween the excited argon atom and the ionizing electron results in anargon ion (Ar⁺) and two electrons.

As previously discussed, the excited argon atoms generally require lessenergy to become ionized than neutral ground state argon atoms. Thus,the excited atoms tend to more rapidly ionize near the surface of theouter cathode section 202 b than the neutral ground state argon atoms.As the density of the excited atoms in the plasma increases, theefficiency of the ionization process rapidly increases. This increasedefficiency eventually results in an avalanche-like increase in thedensity of the high-density plasma. Under appropriate excitationconditions, the proportion of the energy applied to the initial plasma,which is transformed to the excited atoms, is very high for a pulseddischarge in the feed gas 234.

In one mode of operation, the density of the plasma is increased bycontrolling the flow of the feed gas 234 in the region 214. In thisembodiment, a first volume of feed gas 234 is supplied to the region214. The first volume of feed gas 234 is then ionized to form an initialplasma in the region 214. The first power supply 206 then applies ahigh-power electrical pulse across the initial plasma. The high-powerelectrical pulse generates a high-density plasma from the initialplasma.

In another mode of operation, the feed gas 234 continues to flow intothe region 214 after the initial plasma is formed. The initial plasma isdisplaced or transported into the region 252 by a new volume of feed gas234. The second power supply 222 (FIG. 2A) then applies a high-powerelectrical pulse between the inner cathode section 202 a and the secondanode 226.

The density of the plasma is generally limited by the level and durationof the high-power electrical pulse that can be absorbed before thedischarge contracts and terminates. Increasing the flow rate of at leastone of the feed gases 234, 236 can increase the level and duration ofthe high-power electrical pulse that can be absorbed by the discharge.Any type of gas exchange means can be used to rapidly exchange thevolume of feed gas.

Thus, the density of the plasma can be increased by transporting theinitial plasma through the region 214 by a rapid volume exchange of feedgas 234. As the feed gas 234 moves through the region 214 and interactswith the moving initial plasma, it becomes partially ionized from theapplied electrical pulse. Applying a high-power electrical pulse throughthe region 214 can result in an ionization process that includes acombination of direct ionization and/or stepwise ionization as describedherein. Transporting the initial plasma through the region 214 by arapid volume exchange of the feed gas 234 increases the level and theduration of the power that can be applied to the high-density plasmaand, thus, generates a higher density strongly-ionized plasma.

In one embodiment, the plasma generating system 200 can be configuredfor plasma etching. In another embodiment, the plasma generating system200 can be configured for plasma sputtering. In particular, the plasmagenerating system 200 can be configured for sputtering magneticmaterials. Known magnetron sputtering systems generally are not suitablefor sputtering magnetic materials because the magnetic field generatedby the magnetron can be absorbed by the magnetic target material. RFdiode sputtering is sometimes used to sputter magnetic materials.However, RF diode sputtering generally has poor film thicknessuniformity and produces relatively low deposition rates.

The plasma generating system 200 can be adapted to sputter magneticmaterials by including a target assembly (not shown) having a magnetictarget material and by driving that target assembly with an RF powersupply (not shown). For example, an RF power supply can provide an RFpower that is about 10 kW. A substantially uniform initial plasma can begenerated by applying RF power across a feed gas that is locatedproximate to the target assembly. The high-density plasma is generatedby applying a strong electric field across the initial plasma asdescribed herein. The RF power supply applies a negative voltage bias tothe target assembly. Ions in the high-density plasma bombard the targetmaterial thereby causing sputtering.

The plasma generating system 200 can also be adapted to sputterdielectric materials. Dielectric materials can be sputtered by driving atarget assembly (not shown) including a dielectric target material withan RF power supply (not shown). For example, an RF power supply canprovide an RF power that is about 10 kW. A substantially uniform initialplasma can be generated by applying RF power across a feed gas that islocated proximate to the target assembly.

In one embodiment, a magnetic field is generated proximate to the targetassembly in order to trap electrons in the initial plasma. Thehigh-density plasma is generated by applying a strong electric fieldacross the initial plasma as described herein. The RF power supplyapplies a negative voltage bias to the target assembly. Ions in thehigh-density plasma bombard the target material thereby causingsputtering.

A high-density plasma according to the present invention can be used togenerate an ion beam. An ion beam source according to the presentinvention includes the plasma generating system 200 and an externalelectrode (not shown) that is used to accelerate ions in the plasma. Inone embodiment, the external electrode is a grid. The ion beam sourcecan generate a very high-density ion flux. For example, the ion beamsource can generate ozone flux. Ozone is a highly reactive oxidizingagent that can be used for many applications such as cleaning processchambers, deodorizing air, purifying water, and treating industrialwastes, for example.

FIG. 3 illustrates a cross-sectional view of a plasma generatingapparatus 300 including a magnet assembly 302 according to theinvention. The magnet assembly 302 can include permanent magnets 304, oralternatively, electro-magnets (not shown). In one embodiment, themagnet assembly 302 is adapted to create a magnetic field 306 proximateto the inner cathode section 202 a. The configuration of the magnetassembly 302 can be varied depending on the desired shape and strengthof the magnetic field 306. The magnet assembly 302 can have either abalanced or unbalanced configuration.

In one embodiment, the magnet assembly 302 includes switchingelectro-magnets, which generate a pulsed magnetic field proximate to theinner cathode section 202 a. In some embodiments, additional magnetassemblies (not shown) can be placed at various locations around andthroughout the process chamber (not shown).

The magnetic assembly 302 can be configured to generate a magnetic fieldin the shape of one or more racetracks (not shown). Magnetic fields inthe shape of one or more racetracks can improve target utilization insputtering targets by distributing regions of highest target erosionacross the surface of the target. These regions of high target erosiongenerally correspond to locations in which the magnetic field lines areparallel to the surface of the target.

In operation, the magnetic field 306 is generated proximate to the innercathode section 202 a. The permanent magnets 304 continuously generatethe magnetic field 306. Electro-magnets can also generate the magneticfield 306. The strength of the magnetic field 306 can be in the range ofabout fifty gauss to two thousand gauss. After the magnetic field 306 isgenerated, the feed gas 234 from the gas source 238 is supplied betweenthe outer cathode section 202 b and the first anode 210. A volume of thefeed gas 234 fills in the region 214.

Next, the first power supply 206 generates an electric field across thefeed gas 234 to ignite an initial plasma in the region 214. The feed gas234 flows through the region 214 and continuously displaces the initialplasma. The initial plasma diffuses into the region 252′ and themagnetic field 306 traps electrons in the initial plasma. A largefraction of the electrons are concentrated in the region 308 thatcorresponds to the weakest area of the magnetic field 306 that isgenerated by the magnet assembly 302. By trapping the electrons in theregion 308, the magnetic field 306 substantially prevents the initialplasma from diffusing away from the inner cathode section 202 a.

The second power supply 222 generates a strong electric field betweenthe second anode 226 and the inner cathode section 202 a. The strongelectric field super-ionizes the initial plasma to generate ahigh-density plasma having an ion density that is greater than the iondensity of the initial plasma. In one embodiment, the initial plasma hasan ion density that is in the range of about 10⁷ to 10¹² cm⁻³ and thehigh-density plasma has an ion density that is greater than about 10¹²cm⁻³.

The magnetic field 306 can improve the homogeneity of the high-densityplasma. The magnetic field 306 can also increase the ion density of thehigh-density plasma by trapping electrons in the initial plasma and alsoby trapping secondary electrons proximate to the inner cathode section202 a. The trapped electrons ionize excited atoms in the initial plasmathereby generating the high-density plasma. In one embodiment (notshown), a magnetic field is generated in the region 214 thatsubstantially traps electrons in the area where the initial plasma isignited.

The magnetic field 306 also promotes increased homogeneity of thehigh-density plasma by setting up a substantially circular electron ExBdrift current 310 proximate to the inner cathode section 202 a. In oneembodiment, the electron ExB drift current 310 generates a magneticfield that interacts with the magnetic field 306 generated by the magnetassembly 302.

When high-power pulses are applied between the inner cathode section 202a and the second anode 226 secondary electrons are generated from theinner cathode section 202 a that move in a substantially circular motionproximate to the inner cathode section 202 a according to crossedelectric and magnetic fields. The substantially circular motion of theelectrons generates the electron ExB drift current 310. The magnitude ofthe electron ExB drift current 310 is proportional to the magnitude ofthe discharge current in the plasma and, in one embodiment, isapproximately in the range of about three to ten times the magnitude ofthe discharge current.

In one embodiment, the substantially circular electron ExB drift current310 generates a magnetic field that interacts with the magnetic field306 generated by the magnet assembly 302. In one embodiment, themagnetic field generated by the electron ExB drift current 310 has adirection that is substantially opposite to the magnetic field 306generated by the magnet assembly 302. The magnitude of the magneticfield generated by the electron ExB drift current 310 increases withincreased electron ExB drift current 310. The homogeneous diffusion ofthe high-density plasma in the region 252′ is caused, at least in part,by the interaction of the magnetic field 306 generated by the magnetassembly 302 and the magnetic field generated by the electron ExB driftcurrent 310.

In one embodiment, the electron ExB drift current 310 defines asubstantially circular shape for low current density plasma. However, asthe current density of the plasma increases, the substantially circularelectron ExB drift current 310 tends to have a more complex shape as theinteraction of the magnetic field 306 generated by the magnet assembly302, the electric field generated by the high-power pulse, and themagnetic field generated by the electron ExB drift current 310 becomesmore acute. For example, in one embodiment, the electron ExB driftcurrent 310 has a substantially cycloidal shape. The exact shape of theelectron ExB drift current 310 can be quite elaborate and depends onvarious factors.

As the magnitude of the electron ExB drift current 310 increases, themagnetic field generated by the electron ExB drift current 310 becomesstronger and eventually overpowers the magnetic field 306 generated bythe magnet assembly 302. The magnetic field lines that are generated bythe magnet assembly 302 exhibit substantial distortion that is caused bythe relatively strong magnetic field that is generated by the relativelylarge electron ExB drift current 310. Thus, a large electron ExB driftcurrent 310 generates a stronger magnetic field that strongly interactswith and can begin to dominate the magnetic field 306 that is generatedby the magnet assembly 302.

The interaction of the magnetic field 306 generated by the magnetassembly 302 and the magnetic field generated by the electron ExB driftcurrent 310 generates magnetic field lines that are somewhat moreparallel to the surface of the inner cathode section 202 a than themagnetic field lines generated by the magnet assembly 302. The somewhatmore parallel magnetic field lines allow the high-density plasma to moreuniformly distribute itself in the area 252′. Thus, the high-densityplasma is substantially uniformly diffused in the area 252′.

FIG. 4 illustrates a graphical representation 400 of applied power as afunction of time for periodic pulses applied to an initial plasma in theplasma generating system 200 of FIG. 2A. The first power supply 206generates a constant power and the second power supply 222 generatesperiodic power pulses. In one illustrative embodiment, the feed gas 234flows into the region 214 between the outer cathode section 202 b andthe first anode 210 at time t₀, before either the first power supply 206or the second power supply 222 are activated.

The time required for a sufficient quantity of feed gas 234 to flow intothe region 214 depends on several factors including the flow rate of thefeed gas 234 and the desired operating pressure. At time t₁, the firstpower supply 206 generates a power 402 that is in the range of about0.01 kW to 100 kW and applies the power 402 between the outer cathodesection 202 b and the anode 210. The power 402 causes the feed gas 234to become at least partially ionized, thereby generating an initialplasma that can be a pre-ionization plasma as previously discussed. Anadditional volume of feed gas flows into the region 214 (FIG. 2A)between time t₁ and time t₂ substantially displacing the initial plasma.The initial plasma is displaced into the region 252 proximate to theinner cathode section 202 a.

At time t₂, the second power supply 222 delivers a high-power pulse 404to the initial plasma that is in the range of about 1 kW to 10 MWdepending on the volume and characteristics of the plasma and theoperating pressure. The high-power pulse 404 substantially super-ionizesthe initial plasma to generate a high-density plasma. The high-powerpulse 404 has a leading edge 406 having a rise time from t₂ to t₃ thatis approximately in the range of 0.1 microseconds to ten seconds. Inthis embodiment, the second power supply 222 is a pulsed power supply.In some embodiments (not shown), the second power supply 222 can be anRF power supply, an AC power supply, or a DC power supply.

In one embodiment, the pulse width of the high-power pulse 404 is in therange of about one microsecond to ten seconds. The high-power pulse 404is terminated at time t₄. In one embodiment, after the delivery of thehigh-power pulse 404, the power 402 from the first power supply 206 iscontinuously applied to generate additional plasma from the flowing feedgas 234, while the second power supply 222 prepares to deliver anotherhigh-power pulse 408.

At time t₅, the second power supply 222 delivers another high-powerpulse 408 having a rise time from t₅ to t₆ and terminating at time t₇.In one embodiment, the repetition rate of the high-power pulses is inthe range of about 0.1 Hz to 10 kHz. The particular size, shape, width,and frequency of the high-power pulse 408 depend on the processparameters, such as the operating pressure, the design of the secondpower supply 222, the presence of a magnetic field proximate to theinner cathode section 202 a, and the volume and characteristics of theplasma, for example. The shape and duration of the leading edge 406 andthe trailing edge 410 of the high-power pulse 404 are chosen to controlthe rate of ionization of the high-density plasma.

In another embodiment (not shown), the first power supply 206 and/or thesecond power supply 222 are activated at time t₀ before the feed gas 234flows in the region 214. In this embodiment, the feed gas 234 isinjected between the outer cathode section 202 b and the first anode 210where it is ignited by the first power supply 206 to generate theinitial plasma. In this embodiment, the first power supply 202 is a DCpower supply. In other embodiments (not shown), the first power supply202 can an RF power supply, an AC power supply, or a pulsed powersupply.

FIG. 5 illustrates a cross-sectional view of a plasma generatingapparatus 500 including the magnet assembly 302 of FIG. 3 and anadditional magnet assembly 502 according to the invention. Theadditional magnet assembly 502 can include a permanent magnets 504 asshown, or alternatively, electro-magnets (not shown). In one embodiment,the magnet assembly 502 is adapted to create a magnetic field 506proximate to the outer cathode section 202 b. The configuration of themagnet assembly 502 can be varied depending on the desired shape andstrength of the magnetic field 506. The magnet assembly 502 can haveeither a balanced or unbalanced configuration.

In one embodiment, the magnet assembly 502 includes switchingelectro-magnets, which generate a pulsed magnetic field proximate to theouter cathode section 202 b. In some embodiments, additional magnetassemblies (not shown) can be placed at various locations around andthroughout the process chamber (not shown).

One skilled in the art will appreciate that there are many modes ofoperating the plasma generating apparatus 500. In one embodiment, theplasma generating apparatus 500 is operated by generating the magneticfield 506 proximate to the outer cathode section 202 b. In theembodiment shown in FIG. 5, the permanent magnets 504 continuouslygenerate the magnetic field 506. In other embodiments, electro-magnets(not shown) generate the magnetic field 506 by energizing a currentsource (not shown) that is coupled to the electro-magnets. In oneembodiment, the strength of the magnetic field 506 is in the range ofabout fifty gauss to two thousand gauss. After the magnetic field 506 isgenerated, the feed gas 234 from the gas source 238 is supplied betweenthe outer cathode section 202 b and the first anode 210. A volume of thefeed gas 234 fills in the region 214.

Next, the first power supply 206 generates an electric field across thefeed gas 234 to ignite an initial plasma in the region 214. In oneembodiment, the magnetic field 506 substantially traps electrons in theinitial plasma in the region 214. This causes the initial plasma toremain concentrated in the region 214. In one embodiment, the firstpower supply 206 applies a high-power pulse across the initial plasmathereby generating a high-density plasma in the region 214.

The high-power pulse energizes the electrons in the initial plasma. Themagnetic field 506 causes the electrons to move in a substantiallycircular manner creating a substantially circular electron ExB driftcurrent (not shown) proximate to the outer cathode section 202 b. In oneembodiment, the electron ExB drift current generates a magnetic fieldthat interacts with the magnetic field 506 generated by the magnetassembly 502.

The high-power pulses applied between the outer cathode section 202 band the first anode 210 generate secondary electrons from the outercathode section 202 a that move in a substantially circular motionproximate to the inner cathode section 202 a according to crossedelectric and magnetic fields. The substantially circular motion of theelectrons generates the electron ExB drift current. The magnitude of theelectron ExB drift current is proportional to the magnitude of thedischarge current in the plasma and, in one embodiment, is approximatelyin the range of between about three and ten times the magnitude of thedischarge current. As previously discussed, the electron ExB driftcurrent can improve the homogeneity of the high-density plasma in theregion 214.

FIG. 6 illustrates a cross-sectional view of a plasma generatingapparatus 550 including the magnet assembly 302 of FIG. 3 and anadditional magnet assembly 552 according to the invention. Theadditional magnet assembly 552 can include permanent magnets 554, 556,or alternatively, electro-magnets (not shown). In one embodiment, themagnet assembly 552 is adapted to create a magnetic field 558 proximateto the outer cathode section 202 b. The configuration of the magnetassembly 552 can be varied depending on the desired shape and strengthof the magnetic field 558. The magnet assembly 552 can have either abalanced or unbalanced configuration.

The plasma generating apparatus 550 functions similarly to the plasmagenerating apparatus 500 of FIG. 5. However, the magnetic assembly 552that is located proximate to the outer cathode section 202 b generatesmagnetic field lines 560 that are substantially perpendicular to asurface of the outer cathode section 202 b. The perpendicular magneticfield lines 560 completely cross the region 214, thereby trappingsubstantially all of the electrons in the region 214. Thus, the magneticfield 558 can facilitate a more efficient process of generating theinitial plasma in the region 214. Skilled artisans will appreciate thatalternative magnet configurations can be used within the scope of theinvention.

FIG. 7 illustrates a cross-sectional view of another embodiment of aplasma generating apparatus 600 including a magnet assembly 602according to the invention. The magnet assembly 602 can includepermanent magnets 604, or alternatively, electro-magnets (not shown). Inone embodiment, the magnet assembly 602 is adapted to create a magneticfield 606 that is located proximate to the inner cathode section 202 aand proximate to the outer cathode section 202 b. The configuration ofthe magnet assembly 602 can be varied depending on the desired shape andstrength of the magnetic field 606. The magnet assembly 602 can haveeither a balanced or unbalanced configuration.

In one embodiment, the magnet assembly 602 includes switchingelectro-magnets, which generate a pulsed magnetic field proximate to theinner 202 a and the outer cathode sections 202 b. In some embodiments,additional magnet assemblies (not shown) can be placed at variouslocations around and throughout the process chamber (not shown).

In one embodiment, the permanent magnets 604 continuously generate themagnetic field 606. In other embodiments, electro-magnets (not shown)generate the magnetic field 606 by energizing a current source (notshown) that is coupled to the electro-magnets. In one embodiment, thestrength of the magnetic field 606 is in the range of about fifty gaussto two thousand gauss.

In operation, after the magnetic field 606 is generated, the feed gas234 from the gas source 238 is supplied between the outer cathodesection 202 b and the first anode 210. A volume of the feed gas 234fills in the region 214.

Next, the first power supply 206 generates an electric field across thefeed gas 234 that ignites an initial plasma in the region 214. In oneembodiment, electrons in the initial plasma diffuse from the region 214to the region 608 substantially along magnetic field lines 609 generatedby the magnet assembly 602. In one embodiment, the electrons in theinitial plasma are concentrated in the region 608 corresponding to theweakest area of the magnetic field 606 generated by the magnet assembly602. Thus, the initial plasma is concentrated proximate to the outeredge of the inner cathode section 202 a.

The second power supply 222 generates a strong electric field betweenthe second anode 226 and the inner cathode section 202 a. The strongelectric field super-ionizes the initial plasma to generate ahigh-density plasma having an ion density that is greater than the iondensity of the initial plasma. In one embodiment, the initial plasma hasan ion density in the of about 10⁷ to 10¹² cm⁻³. In one embodiment, thehigh-density plasma has an ion density that is greater than about 10¹²cm⁻³.

In one embodiment, the high-density plasma is used in a magnetronsputtering system (not shown). The magnetron sputtering system includesa target (not shown) that can be integrated into the inner cathodesection 202 a. Operating parameters can be chosen such that the outeredge of the target is eroded at a relatively high rate compared with thecenter of the target because the high-density plasma is concentrated inthe region 608. Thus, a sputtering system according to the presentinvention can include a target that is relatively small compared withknown sputtering systems for similarly sized substrates (not shown). Inaddition, the power level of the high-power pulse can be chosen suchthat the high-density plasma can be homogeneously distributed across thetarget as described herein.

The magnetic field 606 can improve the homogeneity of the high-densityplasma and can increase the ion density of the high-density plasma bytrapping electrons in the initial plasma and also trapping secondaryelectrons proximate to the target. The trapped electrons ionize excitedatoms in the initial plasma thereby generating the high-density plasma.The magnetic field 606 also promotes increased homogeneity of thehigh-density plasma by setting up an electron ExB drift current 610proximate to the target. In one embodiment, the electron ExB driftcurrent 610 generates a magnetic field that interacts with the magneticfield 606 generated by the magnet assembly 602 as described herein.

FIG. 8 illustrates a cross-sectional view of a plasma generatingapparatus 650 including a magnet configuration that includes a firstmagnet 652 and a second magnet 654 according to the invention. The first652 and the second magnets 654 can be any type of magnet, such as apermanent ring-shaped magnet or an electro-magnet, for example.

The plasma generating apparatus 650 also includes a segmented cathode656. The segmented cathode 656 (656 a, b) includes an inner cathodesection 656 a and an outer cathode section 656 b. The outer cathodesection 656 b is disposed generally opposite to the inner cathodesection 656 a, but can be offset as shown in FIG. 8. The segmentedcathode 656 illustrated in FIG. 8 can reduce sputtering contaminationcompared with known cathodes used in sputtering systems because both theinner cathode section 656 a and the outer cathode section 656 b caninclude target material (not shown). Consequently, any material that issputtered from the outer cathode section 656 b is target materialinstead of cathode material that could contaminate the sputteringprocess.

The plasma generating apparatus 650 also includes an anode 658. Theanode 658 is disposed proximate to the inner cathode section 656 a andthe outer cathode section 656 b. In one embodiment, the first output 220of the second power supply 222 is coupled to the inner cathode section656 a and the second output 224 of the second power supply 222 iscoupled to an input 660 of the anode 658.

In one embodiment, a first output 662 of a first power supply 664 iscoupled to the outer cathode section 656 b. A second output 666 of thefirst power supply 664 is coupled to the input 660 of the anode 658. Inone embodiment (not shown), the anode 658 is coupled to ground potentialand the second output 224 of the second power supply 222 as well as thesecond output 666 of the first power supply 664 are also coupled toground potential.

The plasma generating apparatus 650 operates in a similar manner to theplasma generating apparatus 200 of FIG. 2A. However, the magnetic field668 generated by the first 652 and the second magnets 654 issubstantially parallel to at least a portion of the surface of the innercathode section 656 a. The shape of the magnetic field 668 can result ina homogeneous plasma volume that is located proximate to the innercathode section 656 a as discussed herein. Additionally, the magneticfield 668 traps substantially all of the secondary electrons from theinner 656 a and the outer cathode sections 656 b due to theconfiguration of the first 652 and the second magnets 654.

In one mode of operation, feed gas 234 from the gas source 238 flows inthe region 214 between the anode 658 and the outer cathode section 656b. In some embodiments, the feed gas source 240 supplies feed gas 236between the inner cathode section 656 a and the anode 658. The firstpower supply 664 generates an electric field across the feed gas 234that generates an initial plasma in the region 214. Electrons in theinitial plasma diffuse along the magnetic field lines of the magneticfield 668. Due to the configuration of the magnets 652 and 654,substantially all of the electrons in the initial plasma are trapped bythe magnetic field 668. The initial plasma diffuses towards the innercathode section 656 a as the feed gas 234 continues to flow.

After a suitable volume of the initial plasma is located proximate tothe inner cathode section 656 a, the second power supply 222 generates astrong electric field between the inner cathode section 656 a and theanode 658. The strong electric field super-ionizes the initial plasmaand generates a high-density plasma having an ion density that is higherthan the ion density of the initial plasma.

FIG. 9 illustrates a cross-sectional view of a plasma generatingapparatus 700 according to the present invention including a segmentedcathode assembly 702 (702 a, b), an ionizing electrode 708, and a first206, a second 222 and a third power supply 704. The first 206, thesecond 222, and the third power supplies 704 can each be any type ofpower supply suitable for plasma generation, such as a pulsed powersupply, a RF power supply, a DC power supply, or an AC power supply. Insome embodiments, the first 206, the second 222, and/or the third powersupplies 704 operate in a constant power or constant voltage mode asdescribed herein.

Only one portion of the segmented cathode assembly 702 is shown forillustrative purposes. In one embodiment, the portion that is not shownin FIG. 9 is substantially symmetrical to the portion shown in FIG. 9.The plasma generating apparatus 700 also includes a first anode 210 anda second anode 706. In one embodiment, the ionizing electrode 708 is afilament-type electrode. The ionizing electrode 708 can be ring-shapedor any other shape that is suitable for generating an initial plasma inthe region 214. Isolators 709 insulate the inner cathode section 702 afrom the outer cathode section 702 b. The isolators 709 also insulatethe second anode 706 from the inner 702 a and the outer cathode sections702 b.

A first output 710 of the third power supply 704 is coupled to theionizing electrode 708. A second output 712 of the third power supply704 is coupled to the outer cathode section 702 b. The power generatedby the third power supply 704 is sufficient to ignite a feed gas 234located in the region 214 to generate an initial plasma.

The first output 204 of the first power supply 206 is coupled to theouter cathode section 702 b. The second output 208 of the first powersupply 206 is coupled to the first anode 210. The power generated by thefirst power supply 206 is sufficient to increase the ion density of theinitial plasma in the region 214.

The first output 220 of the second power supply 222 is coupled to theinner cathode section 702 a. The second output 224 of the second powersupply 222 is coupled to the second anode 706.

In operation, the first power supply 206 is a pulsed power supply thatapplies a high-power pulse between the outer cathode section 702 b andthe first anode 210. The high-power pulse generates an electric field(not shown) through the region 214. The electric field generates ahigh-density plasma from the initial plasma that is generated by theionizing electrode 708. The high-density plasma is generally morestrongly ionized than the initial plasma.

In one embodiment, the feed gas 234 continues to flow after thehigh-density plasma is generated in the region 214. The feed gas 234displaces the high-density plasma towards the inner cathode region 702a. The feed gas exchange continues until a suitable volume of thehigh-density plasma is located proximate to the inner cathode section702 a.

In one embodiment, the second power supply 222 is a pulsed power supplythat applies a high-power pulse across the high-density plasma. Thehigh-power pulse generates an electric field (not shown) between theinner cathode section 702 a and the second anode 706. The electric fieldgenerates a plasma that is generally more strongly-ionized than thehigh-density plasma.

The plasma generating apparatus 700 of the present invention generates avery high-density plasma using standard power supplies. The plasmagenerating apparatus 700 of the present invention can generate a veryhigh-density plasma at a lower cost compared with a known plasmagenerating apparatus because the plasma generating apparatus 700 can userelatively inexpensive and commercially available power supplies. Inplasma sputtering applications, the sputtering targets that are used inthe plasma generating apparatus 700 can be much smaller relative tocomparable sputtering targets that are used in known magnetronsputtering systems used to process similarly sized substrates.

FIG. 10 illustrates a cross-sectional view of a plasma generatingapparatus 720 according to the present invention including a segmentedcathode assembly 722 (722 a, b), a common anode 724, an ionizingelectrode 708, and a first 206, a second 222, and a third power supply704. The first 206, the second 222, and the third power supplies 704 caneach be any type of power supply suitable for plasma generation, such asa pulsed power supply, a RF power supply, a DC power supply, or an ACpower supply. In some embodiments, the first 206, the second 222, and/orthe third power supplies 704 operate in a constant power or constantvoltage mode as described herein.

Only one portion of the segmented cathode assembly 722 is shown forillustrative purposes. In one embodiment, the portion that is not shownin FIG. 10 is substantially symmetrical to the portion shown in FIG. 10.In one embodiment, the ionizing electrode 708 is a filament-typeelectrode. The ionizing electrode 708 can be ring-shaped or any othershape that is suitable for generating an initial plasma in the region214. An isolator 726 insulates the anode 724 from the inner cathodesection 722 a. An isolator 728 insulates the anode 724 from the outercathode section 722 b.

In a plasma sputtering configuration, the segmented cathode assembly 722illustrated in FIG. 10 can reduce sputtering contamination compared withknown cathodes used in sputtering systems because both the inner cathodesection 722 a and the outer cathode section 722 b can include targetmaterial (not shown). Consequently, any material that is sputtered fromthe outer cathode section 722 b is target material instead of cathodematerial that could contaminate the sputtering process.

A first output 710 of the third power supply 704 is coupled to theionizing electrode 708. A second output 712 of the third power supply704 is coupled to the outer cathode section 722 b. The power generatedby the third power supply 704 is sufficient to ignite a feed gas 234located in the region 214 to generate an initial plasma.

The first output 204 of the first power supply 206 is coupled to theanode 724. The second output 208 of the first power supply 206 iscoupled to the outer cathode section 722 b. The power generated by thefirst power supply 206 is sufficient to increase the ion density of theinitial plasma in the region 214.

The first output 220 of the second power supply 222 is coupled to theinner cathode section 722 a. The second output 224 of the second powersupply 222 is coupled to the anode 724.

In operation, the first power supply 206 is a pulsed power supply thatapplies a high-power pulse between the outer cathode section 722 b andthe anode 724. The high-power pulse generates an electric field throughthe region 214. The electric field generates a high-density plasma fromthe initial plasma. The high-density plasma is generally more stronglyionized than the initial plasma.

In one embodiment, the feed gas 234 continues to flow after thehigh-density plasma is generated in the region 214. The feed gas 234displaces the high-density plasma towards the inner cathode region 722a. The feed gas exchange continues until a suitable volume of thehigh-density plasma is located proximate to the inner cathode section722 a.

In one embodiment, the second power supply 222 is a pulsed power supplythat applies a high-power pulse across the high-density plasma. Thehigh-power pulse generates a strong electric field between the innercathode section 722 a and the anode 724. The strong electric fieldgenerates a plasma that is generally more strongly-ionized than thehigh-density plasma.

FIG. 11 illustrates a cross-sectional view of a plasma generatingapparatus 725 according to the present invention including the segmentedcathode assembly 702 (702 a, b) and a first 206, a second 222 and athird power supply 704. The first 206, the second 222, and the thirdpower supplies 704 can each be any type of power supply suitable forplasma generation, such as a pulsed power supply, a RF power supply, aDC power supply, or an AC power supply. In some embodiments, the first206, the second 222, and/or the third power supplies 704 operate in aconstant power or constant voltage mode as described herein. The first206 and the third power supplies 704 can be integrated into a singlepower supply.

Only one portion of the segmented cathode assembly 702 is shown forillustrative purposes. In one embodiment, the portion that is not shownin FIG. 11 is substantially symmetrical to the portion shown in FIG. 11.The plasma generating apparatus 725 also includes a first anode 210 anda second anode 706. Isolators 709 insulate the inner cathode section 702a from the outer cathode section 702 b and insulate the second anode 706from the inner 702 a and the outer cathode sections 702 b.

A first output 710 of the third power supply 704 is coupled to the outercathode section 702 b. A second output 712 of the third power supply 704is coupled to the first anode 210. The power generated by the thirdpower supply 704 is sufficient to ignite a feed gas 234 located in theregion 214 to generate an initial plasma.

A first output 204 of the first power supply 206 is coupled to the outercathode section 702 b. A second output 208 of the first power supply 206is coupled to the first anode 210. A first output 220 of the secondpower supply 222 is coupled to the inner cathode section 702 a. A secondoutput 224 of the second power supply 222 is coupled to the second anode706.

In operation, the power generated by the first power supply 206 issufficient to increase the ion density of the initial plasma in theregion 214 that is generated by the third power supply 704. In oneembodiment, the first power supply 206 is a pulsed power supply thatapplies a high-power pulse between the outer cathode section 702 b andthe first anode 210. The high-power pulse generates an electric fieldthrough the region 214. The electric field generates a high-densityplasma from the initial plasma. The high-density plasma is generallymore strongly ionized than the initial plasma.

In one embodiment, the feed gas 234 continues to flow after thehigh-density plasma is generated in the region 214. The feed gas 234displaces the high-density plasma towards the inner cathode region 702a. The feed gas exchange continues until a suitable volume of thehigh-density plasma is located proximate to the inner cathode section702 a.

In one embodiment, the second power supply 222 is a pulsed power supplythat applies a high-power pulse across the high-density plasma. Thehigh-power pulse generates a strong electric field between the innercathode section 702 a and the second anode 706. The strong electricfield generates a plasma that is generally more strongly-ionized thanthe high-density plasma.

The plasma generating apparatus 725 of the present invention generates avery high-density plasma using standard power supplies. The plasmagenerating apparatus 725 of the present invention can generate a veryhigh-density plasma at a lower cost compared with a known plasmagenerating apparatus because the plasma generating apparatus 725 can userelatively inexpensive and commercially available power supplies.

There are many modes of operation for the plasma generating apparatus725. For example, the first power supply 206 and the second power supply222 can both be operated in constant power mode. In another mode ofoperation, the first power supply 206 is operated in constant power modeand the second power supply 222 is operated in constant voltage mode. Instill another mode of operation, the first 206 and the second powersupplies 222 are both operated in constant voltage mode. Some of thesemodes of operation are discussed in more detail herein.

FIG. 12 illustrates a cross-sectional view of a plasma generatingapparatus 730 according to the present invention including a segmentedcathode assembly 732 (732 a, b), a second anode 706, a first 731 and asecond power supply 222. In this embodiment, the outer cathode sectionis in the form of an excited atom source 732 b. The excited atom source732 b generates excited atoms including metastable atoms from groundstate atoms in the feed gas 234. In another embodiment (not shown), theouter cathode section 732 b is in the form of a hollow cathode. Skilledartisans will appreciate that multiple excited atom sources (not shown)can surround the inner cathode section 732 a.

The first 731 and the second power supplies 222 can be any type of powersupplies suitable for plasma generation, such as pulsed power supplies,RF power supplies, DC power supplies, or AC power supplies. In someembodiments, the first 731 and/or the second power supplies 222 operatein a constant power or constant voltage mode as described herein.

Only one portion of the segmented cathode assembly 732 is shown forillustrative purposes. In one embodiment, the portion that is not shownis substantially symmetrical to the portion shown in FIG. 12. The innercathode section 732 a can be electrically isolated from the excited atomsource 732 b. Isolators 709 insulate the second anode 706 from the innercathode section 732 a and the excited atom source 732 b.

The excited atom source 732 b includes a tube 733. The tube 733 can beformed of non-conducting material, such as a dielectric material, likeboron nitride or quartz, for example. A nozzle 734 is positioned at oneend of the tube 733. The nozzle 734 can be formed from a ceramicmaterial. The tube 733 is surrounded by an enclosure 735. A skimmer 736having an aperture 737, is positioned adjacent to the nozzle 734 forminga nozzle chamber 738. The skimmer 736 can be connected to the enclosure735. In one embodiment, the skimmer 736 is cone-shaped as shown in FIG.12. In one embodiment, the enclosure 735 and the skimmer 736 areelectrically connected to ground potential.

The tube 733 and the enclosure 735 define an electrode chamber 739 thatis in fluid communication with a gas inlet 740. A feed gas source (notshown) is coupled to the gas inlet 740 so as to allow feed gas 234 toflow into the electrode chamber 739. An electrode 741 is positionedinside the electrode chamber 739 adjacent to the nozzle 734 and to theskimmer 736. In one embodiment, the electrode 741 is a needle electrode,as shown in FIG. 12. The needle electrode generates a relatively highelectric field at the tip of the electrode. The electrode 741 iselectrically isolated from the skimmer 736.

A first output 742 of the first power supply 731 is coupled to theneedle electrode 741 with a transmission line 743. An insulator 744isolates the transmission line 743 from the grounded enclosure 735. Asecond output 745 of the first power supply 737 is coupled to ground.

A first output 220 of the second power supply 222 is coupled to theinner cathode section 732 a. A second output 224 of the second powersupply 222 is coupled to the second anode 706. In one embodiment, thesecond power supply 222 generates an electric field between the innercathode section 732 a and the second anode 706.

The plasma generating apparatus 730 of the present invention generates ahigh-density plasma using standard power supplies. The plasma generatingapparatus 730 of the present invention can generate a high-densityplasma at a lower cost compared with known plasma generating apparatusbecause the plasma generating apparatus 730 can use relativelyinexpensive and commercially available power supplies. In addition, thesputtering targets that can be used in the plasma generating apparatus730 can be much smaller relative to comparable sputtering targets thatare used in known magnetron sputtering systems used to process similarlysized substrates.

There are many modes of operation for the plasma generating apparatus730. For example, the first power supply 731 and the second power supply222 can both be operated in constant power mode. In another mode ofoperation, the first power supply 731 is operated in constant power modeand the second power supply 222 is operated in constant voltage mode. Instill another mode of operation, the first 731 and the second powersupplies 222 are both operated in constant voltage mode. Some of thesemodes of operation are discussed in more detail herein.

In one illustrative mode of operation, ground state atoms in the feedgas 234 are supplied to the excited atom source 732 b through the gasinlet 740. The pressure in the electrode chamber 739 is optimized toproduce exited atoms including metastable atoms by adjusting parameters,such as the flow rate of the feed gas 234, the diameter of the nozzle734, and the diameter of the aperture 737 of the skimmer 736. The firstpower supply 731 generates an electric field (not shown) between theneedle electrode 741 and the skimmer 736. The electric field raises theenergy of the ground state atoms to an excited state that generatesexcited atoms. Many of the excited atoms are metastable atoms. Theelectric field can also generate some ions and electrons along with theexited atoms.

Optional magnets 746 generate a magnetic field 747 proximate to theexcited atom source 732 b. The magnetic field 747 can be used to assistin exciting the ground state atoms. The magnetic field 747 trapsaccelerated electrons proximate to the electric field. Some of theaccelerated electrons impact a portion of the ground state atoms,thereby transferring energy to those ground state atoms. This energytransfer excites at least a portion of the ground state atoms to createa volume of excited atoms including metastable atoms.

A portion of the volume of excited atoms as well as some ions, electronsand ground state atoms flow through the nozzle 734 into the nozzlechamber 738 as additional feed gas flows into the electrode chamber 739.A large fraction of the ions and electrons are trapped in the nozzlechamber 738 while the excited atoms and the ground state atoms flowthrough the aperture 737 of the skimmer 736.

After a sufficient volume of excited atoms including metastable atoms ispresent proximate to the inner cathode section 732 a, the second powersupply 222 generates an electric field (not shown) proximate to thevolume of excited atoms between the inner cathode section 732 a and thesecond anode 706. The electric field raises the energy of the volume ofexcited atoms causing collisions between neutral atoms, electrons, andexcited atoms including metastable atoms. These collisions generate theplasma proximate to the inner cathode section 732 a. The plasma includesions, excited atoms and additional metastable atoms. The efficiency ofthis multi-step ionization process increases as the density of excitedatom and metastable atoms increases.

In one embodiment, a magnetic field is generated proximate to the innercathode section 732 a. The magnetic field can increase the ion densityof the plasma by trapping electrons in the plasma and also by trappingsecondary electrons proximate to the inner cathode section 732 a.

All noble gas atoms have metastable states. For example, argonmetastable atoms can be generated by a multi-step ionization process. Ina first step, ionizing electrons e⁻ are generated by applying asufficient voltage across argon feed gas containing ground state argonatoms. When an ionizing electron e⁻ collides with a ground state argon(Ar) atom, a metastable argon atom and an electron are generated. Argonhas two metastable states, see Fabrikant, I. I., Shpenik, O. B.,Snegursky, A. V., and Zavilopulo, A. N., Electron Impact Formation ofMetastable Atoms, North-Holland, Amsterdam. In a second step in themulti-step ionization process, the metastable argon atom is ionized.

The multi-step ionization process described herein substantiallyincreases the rate at which the plasma is formed and, therefore,generates a relatively dense plasma. The rate is increased because onlya relatively small amount of energy is required to ionize the metastableatoms as described herein. For example, ground state argon atoms requireenergy of about 15.76 eV to ionize. However, argon metastable atomsrequire only about 4 eV of energy to ionize. The excited atom source 732b provides the energies of about 11.55 eV and 11.72 eV that arenecessary to reach argon metastable states. Therefore, a volume ofmetastable atoms will ionize at a much higher rate than a similar volumeof ground state atoms for the same input energy.

Furthermore, as the density of the metastable atoms in the plasmaincreases, the efficiency of the ionization process rapidly increases.The increased efficiency results in an avalanche-like process thatsubstantially increases the density of the plasma. In addition, the ionsin the plasma strike the inner cathode section 732 a causing secondaryelectron emission from the inner cathode section 732 a. The secondaryelectrons interact with ground state atoms and with the excited atomsincluding the metastable atoms in the plasma. This interaction furtherincreases the density of ions in the plasma as additional volumes ofmetastable atoms become available. Thus, for the same input energy, thedensity of the plasma that is generated by the multi-step ionizationprocess according to the present invention is significantly greater thana plasma that is generated by direct ionization of ground state atoms.

FIG. 13 illustrates a graphical representation 750 of power as afunction of time for each of a first 206, a second 222, and a thirdpower supply 704 for one mode of operating the plasma generating system700 of FIG. 9. The first 206, second 222, and third power supplies 704are synchronized to each other to optimize certain properties of theplasma. For example, the third power supply 704 generates a constantpower throughout the process, while the first 206 and the second powersupplies 222 generate periodic power pulses at preset intervals.Although FIG. 13 relates to the operation of FIG. 9, skilled artisanswill appreciate that the plasma generating systems 720, 725 of FIG. 10and FIG. 11, respectively, can be operated in a similar manner to theplasma generating system 700 of FIG. 9. In one mode of operation, thefirst power supply 206 and the second power supply 222 are operated in aconstant power mode.

In this mode, the plasma generating apparatus 700 can operate asfollows. At time t₀, the third power supply 704 applies a constant power752 in the range of about 0.1 kW to 10 kW across the feed gas 234 togenerate an initial plasma. The power level required to generate theinitial plasma depends on several factors including the dimensions ofthe region 214, for example. The constant power 752 is applied betweenthe ionizing electrode 708 and the outer cathode section 702 b. Theinitial plasma diffuses towards the inner cathode section 702 a due to apressure differential as described herein. The pressure differentialconcentrates the initial plasma from the region 214 towards the innercathode section 702 a.

At time t₁, the second power supply 222 applies a constant power 754 inthe range of about 0.1 kW to 10 kW across the initial plasma to increasethe ion density of the initial plasma and to sustain the initial plasmaproximate to the inner cathode section 702 a. The time period betweentime t₀ and time t₁ is in the range of about 0.1 msec to 1 sec anddepends on several parameters including the dimensions of the innercathode section 702 a, for example.

At time t₂, a sufficient volume of the initial plasma is locatedproximate to the inner cathode section 702 a and an additional volume ofinitial plasma is generated in the region 214. The first power supply206 then applies a high power pulse 756 across the additional volume ofinitial plasma in the region 214 to generate a high-density plasma inthe region 214. The ion density of the high-density plasma is greaterthan the ion density of the initial plasma. The high-power pulse 756 hasa power level that is in the range of about 10 kW to 1,000 kW. The timeperiod between time t₁ and time t₂ is in the range of about 0.1 msec to1 sec.

The high-density plasma that is generated in the region 214 diffusestoward the inner cathode section 702 a due to the pressure differential.At time t₃, the second power supply 222 applies a high-power pulse 758to the high-density plasma in order to super-ionize the high-densityplasma to further increase the plasma density. The time period betweentime t₂ and time t₃ is in the range of about 0.001 msec to 1 msec. Thetime period of the high-power pulse 758 between time t₃ and time t₄ isin the range of about 0.1 msec to 10 sec.

Additionally, between time t₃ and time t₅, the first power supply 206continues to apply the high-power pulse 756 in order to sustain thehigh-density plasma. At time t₅, the high-power pulse 756 terminates.The second power supply 222 continues to apply a background power 760after the high-power pulse 758 terminates at time t₄. The backgroundpower 760 continues to sustain the high-density plasma. The time periodbetween time t₄ and time t₅ is in the range of about 0.001 msec to 1msec.

At time t₅, the high power pulse 756 generated by the first power supply206 terminates. At time t₆, the first power supply 206 applies anotherhigh-power pulse 762 across a new volume of high-density plasma in theregion 214. The high-power pulse 762 increases the current density inthe new volume of high-density plasma. The new volume of high-densityplasma diffuses towards the inner cathode section 702 a. At time t₇, thesecond power supply 222 applies another high-power pulse 764 to the newvolume of high-density plasma that is located proximate to the innercathode section 702 a. At time t₈, the high-power pulse 764 terminates.At time t₉ the high power pulse 762 from the first power supply 206terminates.

The power from the third power supply 704 is continuously applied for atime that is in the range of about one microsecond to one hundredseconds in order to allow the initial plasma to form and to bemaintained at a sufficient plasma density. The power from the secondpower supply 222 can be continuously applied after the initial plasma isignited in order to maintain the initial plasma. The second power supply222 can be designed so as to output a continuous nominal power in orderto generate and sustain the initial plasma until a high-power pulse isdelivered by the second power supply 222. The high-power pulse has aleading edge having a rise time that is in the range of about 0.1microseconds to ten seconds.

The high-power pulse 756 has a power and a pulse width that issufficient to transform the initial plasma to a strongly-ionizedhigh-density plasma. The high-power pulse 756 is applied for a time thatis in the range of about ten microseconds to ten seconds. The repetitionrate of the high-power pulses 756, 762 is in the range of about 0.1 Hzto 1 kHz.

The particular size, shape, width, and frequency of the high-powerpulses 756, 762 depend on various factors including process parameters,the design of the first power supply 206, the design of the plasmagenerating apparatus 700, the volume of the plasma, and the pressure inthe chamber. The shape and duration of the leading edge and the trailingedge of the high-power pulse 756 is chosen to sustain the initial plasmawhile controlling the rate of ionization of the high-density plasma.

FIG. 14 illustrates a graphical representation 770 of power generated asa function of time for each of a first 206, a second 222, and a thirdpower supply 704 for one mode of operating the plasma generating system700 of FIG. 9. The plasma generating apparatus 700 has many operatingmodes. For example, in this mode, the first power supply 206 is operatedin voltage mode, while the second power supply can be operated in powermode.

In this mode, the plasma generating apparatus 700 can operate asfollows. At time t₀, the third power supply 704 applies a constant power772 in the range of about 0.1 kW to 10 kW across the feed gas 234 togenerate an initial plasma. In one embodiment, the power from the thirdpower supply 704 is continuously applied for a time that is in the rangeof about one microsecond to one hundred seconds in order to allow theinitial plasma to form and to be maintained at a sufficient plasmadensity.

The initial plasma diffuses towards the inner cathode section 702 a. Attime t the second power supply 222 applies a constant power 774 in therange of about 0.1 kW to 10 kW across the initial plasma to increase theion density of the initial plasma and to maintain/sustain the initialplasma proximate to the inner cathode section 702 a.

A pressure differential forces the initial plasma from the region 214towards the inner cathode region 702 a. At time t₂, the first powersupply 206 applies a ramping power pulse 776 across the initial plasmain the region 214 in order to generate a high-density plasma in theregion 214. The ramping power pulse 776 has a power and a rise time thatis sufficient to transform the initial plasma to a strongly-ionizedhigh-density plasma.

The ramping power pulse 776 has a power that is in the range of about 10kW to 1,000 kW and the ramping power pulse 776 is applied for a timethat is in the range of between about ten microseconds to ten seconds.The repetition rate between the ramping power pulses 776 is betweenabout 0.1 Hz and 1 kHz. The shape and duration of the leading edge andthe trailing edge of the ramping power pulse 776 is chosen to sustainthe initial plasma while controlling the rate of ionization of thehigh-density plasma. The high-density plasma diffuses toward the innercathode section 702 a.

At time t₃, the second power supply 222 applies a high-power pulse 778to the high-density plasma to generate a higher-density plasma. At timet₄, the high-power pulse and the ramping power pulse 776 terminate. Thesecond power supply 222 continues to apply a background power 780 tosustain the plasma after the high-power pulse 778 terminates. The secondpower supply 222 can be designed so as to generate a continuous nominalpower that generates and sustains the initial plasma until a high-powerpulse is delivered by the second power supply 222. In one embodiment,the high-power pulse has a leading edge with a rise time that is in therange of about 0.1 microseconds to ten seconds.

At time t₅, the first power supply 206 applies another ramping powerpulse 782 across an additional volume of initial plasma in the region214. The ramping power pulse 782 increases the current density in theadditional volume of initial plasma to generate a high-density plasma.At time t₆, the second power supply 222 applies another high-power pulse784 to the high-density plasma that is located proximate to the innercathode section 702 a. The high-power pulse generates a higher densityplasma proximate to the inner cathode section 702 a. At time t₇, thehigh-power pulse 784 and the ramping power pulse 782 terminate. In oneembodiment, the repetition rate between the ramping power pulses 776,782 is between about 0.1 Hz and 1 kHz.

FIG. 15 illustrates a graphical representation 790 of power as afunction of time for each of a first 206, a second 222, and a thirdpower supply 704 for one mode of operating the plasma generating system700 of FIG. 9. In this mode, the second power supply 222 is a RF powersupply. A RF power supply can be used in plasma sputtering systems forsputtering magnetic materials or dielectric materials, for example. Inthis mode of operation, the first power supply 206 is operated in aconstant power mode. Due to the nature of a RF power supply, the secondpower supply 222 is operated in a substantially constant power mode.

In this mode, the plasma generating apparatus 700 can operate asfollows. At time t₀, the third power supply 704 applies a constant power752 in the range of about 0.1 kW to 10 kW across the feed gas 234 togenerate an initial plasma. The power level required to generate theinitial plasma depends on several factors including the dimensions ofthe region 214, for example. The constant power 752 is applied betweenthe ionizing electrode 708 and the outer cathode section 702 b. Theinitial plasma diffuses towards the inner cathode section 702 a due to apressure differential as described herein. The pressure differentialforces the initial plasma from the region 214 towards the inner cathodesection 702 a.

At time t₁, the second power supply 222 applies an RF driving voltagecorresponding to a power 792 in the range of about 0.1 kW to 10 kWacross the initial plasma to sustain the initial plasma proximate to theinner cathode section 702 a. The RF power supply generates a series ofvery short sinusoidal voltage pulses having a time period between timet₀ and time t₁ that is in the range of about 0.1 msec to 1 sec and thatdepends on several parameters, such as the dimensions of the innercathode section 702 a.

At time t₂, a sufficient volume of the initial plasma is locatedproximate to the inner cathode section 702 a and an additional volume ofinitial plasma is generated in the region 214. The first power supply206 then applies a high-power pulse 756 across the additional volume ofinitial plasma in the region 214 to generate a high-density plasma inthe region 214. The ion density of the high-density plasma is greaterthan the ion density of the initial plasma. The high-power pulse 756 hasa power level that is in the range of about 10 kW to 1,000 kW. In oneembodiment, the time period between time t₁ and time t₂ is in the rangeof about 0.1 msec to 1 sec.

The high-density plasma that is generated in the region 214 diffusestoward the inner cathode section 702 a due to the pressure differential.At time t₃, the second power supply 222 applies a high-power RF pulse794 to the high-density plasma. The high-power RF pulse super-ionizesthe high-density plasma, thereby generating a higher-density plasma. Inone embodiment, the frequency of the high-power pulse 794 is 13.56 MHz.In other embodiments, the frequency of the high power RF pulse 794 is inthe range of about 40 kHz to 100 MHz.

In one embodiment, the time period between time t₂ and time t₃ is in therange of about 0.001 msec to 1 msec. The total time period of thehigh-power pulse 794 between time t₃ and time t₄ is in the range ofabout 0.01 microsec to 10 sec.

Additionally, between time t₃ and time t₅, the first power supply 206continues to apply the high-power pulse 756 in order to maintain thehigh-density plasma. At time t₅, the high-power pulse 756 terminates. Inone embodiment, the second power supply 222 continues to apply abackground RF driving voltage corresponding to a power 796 after thehigh-power pulse 794 terminates at time t₄. The background RF power 796continues to maintain the high-density plasma. The time period betweentime t₄ and time t₅ is in the range of about 0.001 msec to 1 msec.

At time t₆, the first power supply 206 applies another high-power pulse762 across a new volume of initial plasma in the region 214. Thehigh-power pulse 762 generates a new volume of high-density plasma. Thenew volume of high-density plasma diffuses towards the inner cathodesection 702 a. At time t₇, the second power supply 222 applies RFdriving voltage corresponding to another high-power pulse 798 to the newvolume of high-density plasma that is located proximate to the innercathode section 702 a. At time t₈, the high-power pulse 798 terminates.At time t₉, the high power pulse 762 from the first power supply 206terminates.

The power 752 from the third power supply 704 is continuously appliedfor a time that is in the range of about one microsecond to one hundredseconds in order to allow the initial plasma to form and to bemaintained at a sufficient plasma density. In one embodiment, the RFpower from the second power supply 222 is continuously applied after theinitial plasma is ignited in order to maintain the initial plasma.

The high-power pulse 756 has a power and a pulse width that issufficient to transform the initial plasma to a strongly-ionizedhigh-density plasma. The high-power pulse 756 is applied for a time thatis in the range of about ten microseconds to ten seconds. The repetitionrate of the high-power pulses 756, 762 is in the range of about 0.1 Hzto 1 kHz.

The particular size, shape, width, and frequency of the high-powerpulses 756, 762 depend on various factors including process parameters,the design of the first power supply 206, the design of the plasmagenerating apparatus 700, the volume of the plasma, and the pressure inthe chamber, for example. The shape and duration of the leading edge andthe trailing edge of the high-power pulse 756 is chosen to sustain theinitial plasma while controlling the rate of ionization of thehigh-density plasma.

FIG. 16A through FIG. 16C are flowcharts 800, 800′, and 800″ ofillustrative processes of generating high-density plasmas according tothe present invention. Referring to FIG. 16A, the feed gas 234 (FIG. 2)flows into the region 214 (step 802). The feed gas 234 flows through theregion 214 towards the inner cathode section 202 a. Next, the firstpower supply 206 generates a voltage across the feed gas 234 in theregion 214 (step 804). The voltage generates an electric field that islarge enough to ignite the feed gas 234 and generate the initial plasma.While the initial plasma is being generated, additional feed gas flowsinto the region 214 forcing the initial plasma to diffuse proximate tothe inner cathode section 202 a (step 806).

After a suitable volume of the initial plasma is present in the region252, the second power supply 222 generates a large electric field acrossthe initial plasma that super-ionizes the initial plasma, therebygenerating a high-density plasma in the region 252 (step 808). Thehigh-density plasma is typically more strongly ionized than the initialplasma.

In the process illustrated in FIG. 16B, the feed gas 234 flows into theregion 214 (step 802). In one embodiment, the feed gas 234 flows throughthe region 214 towards the inner cathode section 202 a. Next, the firstpower supply 206 generates a voltage across the feed gas 234 in theregion 214 (step 804). The voltage is large enough to ignite the feedgas 234 and to generate the initial plasma. While the initial plasma isbeing generated, additional feed gas 234 flows into the region 214forcing the initial plasma to diffuse proximate to the inner cathodesection 202 a (step 806).

Once the initial plasma is generated in the region 214, the first powersupply 206 generates a strong electric field across the initial plasma,thereby super-ionizing the initial plasma and creating a high-densityplasma in the region 214 (step 810). In one embodiment, an additionalpower supply (not shown) generates the strong electric field instead ofthe first power supply 206.

The high-density plasma diffuses towards the inner cathode section 202 awhere it commingles with the initial plasma in the region 252 (step812). When a suitable volume of the combined plasma is present in theregion 252, the second power supply 222 generates a strong electricfield across the plasma in the region 252 that generates a high-densityplasma (step 814). The high-density plasma will typically be morestrongly-ionized than the plasma formed from the combination of theinitial plasma and the high-density plasma from the region 214.

In the embodiment illustrated in FIG. 16C, the feed gas 234 flows intothe region 214 (step 816). In one embodiment, the feed gas 234 flowsthrough the region 214 towards the inner cathode section 202 a. Next,the first power supply 206 generates a voltage across the feed gas 234in the region 214 (step 818). The voltage generates an electric fieldthat is large enough to ignite the feed gas 234 and generate the initialplasma. In this embodiment, additional feed gas 234 is not supplied tothe region 214 and therefore, the initial plasma remains in the region214.

Once the initial plasma is generated in the region 214, the first powersupply 206 generates a strong electric field across the initial plasma,thereby super-ionizing the initial plasma and creating a high-densityplasma in the region 214 (step 820). In one embodiment, an additionalpower supply (not shown) generates the strong electric field instead ofthe first power supply 206. Once the high-density plasma is present inthe region 214, additional feed gas 234 is supplied to the region 214,displacing the high-density plasma towards the inner cathode section 202a (step 822).

When a suitable volume of high-density plasma is present in the region252, the second power supply 222 generates a strong electric fieldacross the high-density plasma in the region 252 to generate ahigher-density plasma (step 824). The higher-density plasma willtypically be more strongly-ionized than the high-density plasma from theregion 214.

While the invention has been particularly shown and described withreference to specific preferred embodiments, it should be understood bythose skilled in the art that various changes in form and detail may bemade therein without departing from the spirit and scope of theinvention as defined herein.

1-46. (canceled)
 47. A plasma source comprising: a) a cathode assembly comprising an inner cathode section and an outer cathode section; b) a first anode that is positioned adjacent to the outer cathode section and forming a gap there between; and c) a power supply that generates a first electric field across the gap between the first anode and the outer cathode section and that generates a second electric field between the inner cathode section and a second anode, the first electric field ionizing a volume of feed gas that is located in the gap, thereby generating an initial plasma, the second electric field super-ionizing the initial plasma to generate a plasma comprising a higher density of ions than the initial plasma.
 48. The plasma source of claim 47 wherein the first and the second anodes comprise a single anode.
 49. The plasma source of claim 47 wherein the power supply is chosen from the group comprising a pulsed DC power supply, an AC power supply, a DC power supply, and a RF power supply.
 50. The plasma source of claim 47 wherein the power supply further generates a third electric field across the gap between the first anode and the outer cathode section, the third electric field super-ionizing the initial plasma that is located in the gap.
 51. The plasma source of claim 47 wherein at least one of the first and the second electric fields is chosen from the group comprising a static electric field, a pulsed electric field, and a quasi-static electric field.
 52. The plasma source of claim 47 wherein the initial plasma comprises a weakly-ionized plasma.
 53. The plasma source of claim 47 wherein the plasma comprising the higher density of ions than the initial plasma comprises a strongly-ionized plasma.
 54. The plasma source of claim 47 wherein the second electric field generates excited atoms in the initial plasma and generates secondary electrons from the inner cathode section, the secondary electrons ionizing the excited atoms, thereby creating a plasma comprising a higher density of ions than the initial plasma.
 55. The plasma source of claim 47 further comprising a gas valve that opens to exchange the initial plasma with a second volume of feed gas as the power supply generates the first electric field across the second volume of feed gas, thereby increasing an ion density of the plasma.
 56. The plasma source of claim 47 wherein the power supply generates at least one of the first and the second electric fields with a constant power.
 57. The plasma source of claim 47 wherein the power supply generates at least one of the first and the second electric fields with a constant voltage.
 58. The plasma source of claim 47 further comprising a magnet assembly that is positioned to generate a magnetic field proximate to at least one of the inner and the outer cathode sections, the magnetic field trapping electrons in at least one of the initial plasma and the plasma comprising the higher density of ions than the initial plasma.
 59. A plasma source comprising: a) a cathode assembly comprising an inner cathode section; b) an excited atom source that is positioned adjacent to the inner cathode section, the excited atom source generating an initial plasma comprising excited atoms from a volume of feed gas; and c) a power supply that generates an electric field between the inner cathode section and an anode, the electric field super-ionizing the initial plasma to generate a plasma comprising a higher density of ions than the initial plasma.
 60. The plasma source of claim 59 wherein the excited atom source comprises a metastable atom source that generates metastable atoms from the volume of feed gas.
 61. The plasma source of claim 59 wherein the initial plasma comprises a weakly-ionized plasma.
 62. The plasma source of claim 59 wherein the plasma comprising the higher density of ions than the initial plasma comprises a strongly-ionized plasma.
 63. The plasma source of claim 59 further comprising a gas valve that injects feed gas directly between the inner cathode section and the anode.
 64. The plasma source of claim 59 wherein the power supply generates the electric field with a constant power.
 65. The plasma source of claim 59 wherein the power supply generates the electric field with a constant voltage.
 66. The plasma source of claim 59 further comprising a magnet assembly that is positioned to generate a magnetic field proximate to at least one of the inner cathode section and the excited atom source, the magnetic field trapping electrons in at least one of the initial plasma and the plasma comprising the higher density of ions than the initial plasma.
 67. The plasma source of claim 59 wherein the inner cathode section comprises target material for sputtering.
 68. A method of generating a high-density plasma, the method comprising: a) generating a first electric field across a gap between a first anode and an outer cathode section, the first electric field ionizing a volume of feed gas that is located in the gap, thereby generating an initial plasma in the gap; and b) generating a second electric field between a second anode and an inner cathode section, the second electric field super-ionizing the initial plasma, thereby generating a plasma comprising a higher density of ions than the initial plasma.
 69. The method of claim 68 wherein the generating the second electric field between the second anode and the inner cathode section generates excited atoms in the initial plasma and generates secondary electrons from the inner cathode section, the secondary electrons ionizing the excited atoms, thereby creating the plasma comprising the higher density of ions than the initial plasma.
 70. The method of claim 68 wherein at least one of the first and the second electric fields is chosen from the group comprising a static electric field, a quasi-static electric field, and a pulsed electric field.
 71. The method of claim 68 further comprising generating a magnetic field proximate to at least one of the inner and outer cathode sections, the magnetic field trapping electrons in at least one of the initial plasma and the plasma comprising the higher density of ions than the initial plasma.
 72. The method of claim 71 wherein the magnetic field comprises magnetic field lines that are substantially parallel to at least one of the inner and the outer cathode sections.
 73. The method of claim 68 wherein the presence of the initial plasma reduces a probability of developing an electrical breakdown condition between the second anode and the inner cathode section after the second electric field is generated. 